STS testing group

Users who use hearing aids always complain that when someone near the phone often hear hearing aids get "Kaka" noise, this indicates that the phone and hearing aids may not be compatible. According to this situation in September 2006, the US FCC for the mobile phone manufacturers to enforce the HAC (Hearing Aid Compatibility) certification program, the HAC reference standard for the ANSI C63.19 (US wireless communications equipment and hearing aid compatibility measurement countries Standard method). According to the standard definition of consumers through the hearing aid anti-interference level and the corresponding mobile phone signal transmission level to determine a model of hearing aids and mobile phone compatibility.

HAC test plan requires the limit of the measured mobile phone in the M3 (test results are divided into M1 ~ M4). Limit the specific definition of the text will be described later. In addition to HAC, T-coil (audio test) must also require a limit of T3 (test results are divided into T1 ~ T4) range.
The HAC test system of the STS LAB can complete its RF test and electromagnetic field signal requirements according to the HAC standard. The test range includes wireless communication equipment (WD) and hearing aid (HA) Test the frequency of 800 ~ 950MHz and 1.6 ~ 2GHz between the communications products. The cordless phone, mobile phone, personal communication service (PCS), etc. at this frequency can be HAC certified.

Simple test flow for electric and magnetic fields (near-field radiation test flow for wireless communication equipment):

Make sure the probe and test instrument are working properly
WD Configures WD to work in the transmit state

Initialize field strength probe for area scan

OK to exclude the area, set the quarantine to rescan the other areas, and record the largest reading

Both the electric field and the magnetic field are scanned

Confirm and record the classification

If necessary, re-scan the electric field and the magnetic field

The main measuring instruments used are

1. Near field electric field probe
2. Near field magnetic field probe;
3. warhead positioning device;
4. A support system for a wireless communication device (WD);
5. RF equipment and other auxiliary equipment;

In the near field test, the near field probe uses an electric field probe or a magnetic field probe to scan the maximum field strength of the measurement area in the area of 5 cm * 5 cm, respectively. In the multiple pulse periods, the average field strength of the measured object can be obtained by calculating the peak value based on the measured mean value and the known duty ratio of the wireless communication device. The closest distance between the probe and the wireless communication device reference plane must be 1.0 cm.

The following steps must be performed by the wireless communication device before performing the near field radiation test

1. In the wireless communication device modulation mode, calibrate the electric field and the magnetic field probe peak reading;
2. Check to confirm the repeatability and accuracy of the probe positioning system;
3. Confirm that the reflection interference of the measured object is 20 dB or more lower than the desired signal, which can be achieved by repeating the measurement of the same wireless communication device in multiple positions and directions. The difference in readings caused by the reflection must not be greater than ± 0.8 dB;

After confirming that the probe and test instrument are working properly and the wireless communication device is in transmit mode, the field strength probe can be initialized and scanned for the area. The system will automatically record the maximum reading (V / m or A / m). Will be classified according to the following table.


AWF (dB)
Limits for E-Field Emission (V/m)
Limits for H-Field Emission (A/m)


631.0 - 1122.0
1.91 - 3.39


473.2 - 841.4
1.43 - 2.54


354.8 - 631.0
1.07 - 1.91


266.1 - 473.2
0.80 - 1.43


199.5 - 354.8
0.6 - 1.07


149.6 - 266.1
0.45 - 0.80




Table 1 Limit requirements

HAC (hearing aid compatibility) The electric field and magnetic field test of the wireless communication equipment are briefly introduced. In this issue, the T-coil requirements of the wireless device in the audio band in the HAC test are briefly introduced.
HAC detection based on the standard ANSI-C63-19, GB for the YD / T 1643-2007. In the measurement of the magnetic field strength of the wireless communication device in the audio band, we need to test and evaluate the three values. The first magnitude is the magnetic field density of the intentional signal (system signal) at the center frequency of the audio band, and the second The third magnitude is the difference between the intentional signal (system signal) and the unintentional signal (interfering signal) magnetic field field strength.

Figure 1 T-COIL magnetic field test settings

T-Coil test and measurement instruments include the following equipment

1. Base station simulator / RF communication tester that supports audio input or output
2. Probe coil assembly
3. True RMS voltage meter
4.1 / 3 octave bandpass filter
5. Power supply
6. Helmholtz calibration coil

The HAC detection method is to control the wireless communication device to make it in the call mode, and the base station simulator is required to provide the analog audio signal to the wireless communication device. The base station simulator controls the wireless communication device to be in the maximum transmit power state. This is mainly due to its impact in the maximum power mode accurately into the baseband part of the coil may have the impact. It should be noted that the measurement requires the use of RF cable to link rather than through the wireless method of linking, which is mainly to shield the measurement process of radio frequency transmission signal on the measurement results caused by the impact.
The entire test procedure is performed by the following multilevel procedure, first measuring the field field strength of the audio band useful for the hearing aid T-coil. The second step measures the unintentional signal magnetic field component to determine the effect of the audio signal from the wireless communication device display and the battery current path. The following is the general process of measurement (wireless communication equipment audio frequency band magnetic signal test process):

1. Determine the calibration of the measuring instrument
2. Set and verify the test configuration to determine the reference value

Measure the intentional audio band signal
Measure unintentional audio band signals

1. signal quality
2. Magnetic field strength
3. Frequency                  

Identify and record classification information

The purpose of the HAC certification is to avoid the impact of the electromagnetic field formed by the digital mobile telephone on the periphery of the antenna during the communication process for the hearing aid used by the disabled. DeHua Testing Center HAC testing laboratory is the third to provide third-party HAC testing and certification of the laboratory, which fully meet the American Standard ANSI-C63-19 and GB YD / T 1643-2007 test requirements, and has been for the domestic mobile phone Enterprises to complete a large number of HAC testing and pre-research work to ensure that its communications products in line with the protection of people with disabilities requirements.

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